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2011 HSC Notes from the Marking Centre – Senior Science

Contents

Introduction

This document has been produced for the teachers and candidates of the Stage 6 course in Senior Science. It contains comments on candidate responses to the 2011 Higher School Certificate examination, indicating the quality of the responses and highlighting their relative strengths and weaknesses.

This document should be read along with the relevant syllabus, the 2011 Higher School Certificate examination, the marking guidelines and other support documents developed by the Board of Studies to assist in the teaching and learning of Senior Science.

General comments

Teachers and candidates should be aware that examiners may ask questions that address the syllabus outcomes in a manner that requires candidates to respond by integrating their knowledge, understanding and skills developed through studying the course, including the prescribed focus areas. It is important to understand that the Preliminary course is assumed knowledge for the HSC course.

Candidates need to be aware that the marks allocated to the question and the answer space (where this is provided on the examination paper) are guides to the length of the required response. A longer response will not in itself lead to higher marks. Writing in excess of the space allocated may reduce the time available for answering other questions.

Candidates need to be familiar with the Board’s Glossary of Key Words, which contains some terms commonly used in examination questions. However, candidates should also be aware that not all questions will start with or contain one of the key words from the glossary. Questions such as ‘how?’, ‘why?’ or ‘to what extent?’ may be asked or verbs may be used that are not included in the glossary, such as ‘design’, ‘translate’ or ‘list’.

Section I – Core

Part B

Question 21

  1. In better responses, candidates provided two good reasons or one reason and an explanation for using UHMWPE in a hip joint.

    In some weaker responses, candidates included vague or non-specific reasons, such as saying that UHMWPE was better. Some candidates incorrectly thought that UHMWPE was a metal.

  2. In better responses, candidates noted that the growth of the bone onto the roughened stem of the implant was only possible in a young person with actively growing bones. They noted that this is a preferred method because the result is stronger and more suitable for a younger person’s active lifestyle.

    Many candidates knew the difference between cemented and uncemented hip joints and the difference in implanting procedures, but they did not provide a justification and so were unable to score full marks.

    In some weaker responses, candidates incorrectly thought that an uncemented joint was chosen because it could easily be taken out and replaced in the future as the teenager got older. Other weaker responses incorrectly inferred that any hip joint replacement for a young person would only be temporary because the joint will regrow back to its original state.

Question 22

Most candidates provided advantages of tablets and subdermal implants as methods of administering medication.

In better responses, candidates realised that they needed to provide more than one advantage for each method. They also included detail with respect to the advantages, sometimes presenting their answers in tabular form.

In weaker responses, candidates only identified one advantage or bundled together advantages of tablets and subdermal implants without identifying which advantage was associated with which method.

Question 23

In better responses, candidates identified two or more properties of microwaves and then related these properties to the use of microwaves for satellite communication.

Most candidates identified properties of microwaves but many did not justify their use for satellite communication and so did not score top marks.

In weaker responses, candidates confused wavelength and frequency, or related microwave use to land-based communication rather than satellite communication.

Question 24

  1. In better responses, candidates proposed a logical method, identifying an appropriate indicator and relating this to the concept of a pH scale. They also included a safe working practice, repetition or quantitative guidelines.

    Candidates used a wide variety of terminology to describe the indicator used, the most common being a Universal Indicator. They also referred to litmus paper, pH probes and data loggers.

Question 25

  1. In better responses, candidates used their knowledge that a heart attack results from a lack of oxygen to the heart muscle.

    In weaker responses, candidates argued that a heart attack is caused by the heart working harder/faster or by a blockage alone.

  2. In better responses, candidates described both balloon angioplasty and bypass surgery.

    In weaker responses, candidates made general statements about medication, surgery or diet.

  3. Many candidates gained full marks. However, a significant number of candidates did not differentiate between first-hand and secondary sources.

    Better responses clearly showed an understanding of secondary sources.

    Weaker responses focused on conducting first-hand investigations or on the repetition of information, rather than on the reliability of the actual source.

Question 26

  1. Most candidates demonstrated competent skills in constructing a timeline with four or five events.

    In weaker responses, candidates listed events in sequence only but with no scale.

  2. In better responses, candidates included negative and positive impacts, thus making their assessment clear.

    In weaker responses, candidates identified the uses of mobile phones rather than dealing with their impact on society.

Question 27

  1. Correct responses outlined both a verbal and a non-verbal form of communication.

    Some candidates outlined or identified only one verbal or one non-verbal form of communication.

  2. In better responses, candidates correctly showed the energy changes associated with two information systems and identified applications of both of these forms of communication.

    Some candidates only identified one application or one energy transformation associated with one information system.

Question 28

  1. In better responses, candidates correctly constructed a graph from the given data, plotting points and labelling axes correctly.

    In weaker responses, candidates correctly plotted some points and/or correctly labelled one axis.

  2. In better responses, candidates correctly identified the type of mixture and gave a justification for the observations made in the experiment.

    In weaker responses, candidates identified the type of mixture but did not supply a justification, or simply explained the observed results.

Question 29

In better responses, candidates made a clear and explicit reference to the features in the diagram. They also explained the formation of an emulsion by referring to the properties of the emulsifier on the two components of the mixture (eg the oil AND the water).

In weaker responses, candidates only gave an example of an emulsion (eg mayonnaise). These responses did not make specific reference to the diagram.

Question 30

A significant number of candidates understood the purpose of biomedical devices and made good links between increased knowledge of the body and the development and design of biomedical devices.

In better responses, candidates included at least three examples of different devices and related the structure or function of the device to how the body works. These candidates also used appropriate and specific scientific terminology to support their answers.

Weaker responses used a timeline to plot the development of biomedical devices.

Section II – Options

General comments

Candidates are reminded that they should answer only one option.

Question 31 – Polymers

    1. Most responses defined a synthetic as one that is manufactured.

    2. In better responses, candidates identified several similarities and differences between the two polymers. For example, many indicated that polystyrene can be ‘foamed’ for use as a shock-absorbing packing material. Most stated that polyethylene is tougher and more flexible than polystyrene. Many stated that polystyrene is not as recyclable as polyethylene.

      Weaker responses stated that both polymers are flammable or both are light in weight.
  2. In better responses, candidates identified that the melting indicated that the plate was a thermoplastic and that its recyclability depended on the amount and type of named additives.

    Weaker responses described the plate melting and reforming. Several stated that the plate was decomposing.

    1. In better responses, candidates either stated the ingredients and steps taken to make a ‘natural’ polymer, such as ‘playdough’, or described how natural polymers, such as wool, silk and cotton, are formed.

    2. In better responses, candidates chose Kevlar as the most suitable polymer and justified their decision by referring to evidence in the table and relating it to the use of mountain bikes.
    1. In better responses, candidates listed many uses of polymers, such as packaging, car parts, furniture, toys, computers and hip replacements, and explained their benefits to society.

      Weaker responses stated that polymers were cheap or easy to make but did not explain how they benefited society.

    2. In better responses, candidates defined the term ‘biodegradability’ and identified similarities and differences in the biodegradability of items made of wood, metal and plastic produced before and after 1950.

      In weaker responses, candidates did not understand the term ‘biodegradability’.
  5. In better responses, candidates described a range of problems and one or two solutions. Most included the development of biodegradable plastic bags and improved manufacturing processes, along with several strategies for recycling or reducing the amount of plastics used in society. Some candidates referred to the use of fossil fuels in manufacturing as leading to increased atmospheric carbon dioxide and thus contributing to global warming.

    In weaker responses, candidates mentioned environmental issues, such as low biodegradability, recycling, the use of resources, and greenhouse gas emissions, but did not indicate how associated problems had been minimised or eliminated.

Question 32 – Preservatives and Additives

    1. Most candidates named two additives.

    2. In better responses, candidates clearly showed how two preservation techniques increase shelf life, including by inhibiting the growth of microorganisms.

      Weaker responses identified one technique.
  2. In better responses, candidates identified three purposes of additives, naming the typed additive and what it was used for (eg adding humectants to improve the texture).

    In weaker responses, candidates described examples, such as adding colour or flavour to make food more appealing.

    1. In better responses, candidates correctly identified the dependent variable and calculated the change, showing working out.

      Weaker responses did not identify the correct variable or show correct calculations.

    2. In better responses, candidates showed an understanding of valid experimental design to identify three improvements to the experiment design, such as the need to have only one variable changing and the rest controlled.

      In weaker responses, candidates tended just to propose repeating the experiment to make it more reliable.
    1. Most candidates identified the three components of the model of osmosis.

    2. In better responses, candidates showed a clear understanding of osmosis – the movement of water across a semi-permeable membrane – and referred to this model by describing what X, Y and Z do.

      Some responses confused the diagram with bacterial growth.
  5. In better responses, candidates identified some causes of food spoilage, such as bacterial growth, and related this to a range of government regulations to address this, such as those involving use-by dates and storage conditions.

    Weaker responses discussed labelling on foods without relating it to spoilage.

Question 33 – Pharmaceuticals

    1. In better responses, candidates identified the brain and the spinal cord as components of the central nervous system.

      Some candidates incorrectly identified one or two components of the peripheral nervous system, such as the sensory and motor neurones.

    2. While most candidates correctly identified at least one similarity in the pathways, many were unclear about the role of the brain in each pathway.

      In many better responses, candidates used flow charts to show the pathways, clearly indicating at least two components common to both, while correctly indicating the difference as being the absence of a pathway to the brain in the ‘finger in the flame’ reflex arc.

  2. In better responses, candidates referred to the features of the circulatory system that make it suitable for transporting pharmaceuticals, such as various modes of entry, blood acts as a solvent, speed, efficient and bulk distribution, and reaching all the cells.

    In weaker responses, candidates often addressed only one of these features or used simplistic statements, such as ‘around the body’ instead of the more specific ‘to all the cells’.

    1. Most candidates correctly identified a variable, such as temperature, and outlined its effect on the rate of reproduction of bacteria.

    2. In better responses, candidates correctly explained how penicillin interferes with bacterial cell wall formation during binary fission and related this role to its effectiveness in preventing the reproduction of the faster dividing Bacteria X but not the slower dividing Y.

      In weaker responses, candidates did not refer to the stimulus material about doubling rates of the two bacteria and often used weak terminology, such as ‘immunity’, in an attempt to explain how Bacteria Y may have become resistant to penicillin. Some responses incorrectly saw penicillin’s role as regulating the rate of reproduction in bacteria.
    1. Most candidates correctly interpreted the diagram and identified at least two characteristics of the inflammation response.

    2. In better responses, candidates gave features of the advantages and disadvantages of the inflammation response. Many candidates presented this information clearly in a table.
  5. In better responses, candidates showed a thorough understanding of a variety of benefits and problems of using pharmaceuticals, including medical, economic and social issues. They also gave examples of pharmaceuticals, such as analgesics and antibiotics, related their effects to their use, and employed correct scientific terminology.

    In many weaker responses, candidates identified benefits and problems without providing examples to support their statements.

Question 34 – Disasters

    1. In better responses, candidates clearly defined ‘natural disaster’, including reference to both ‘natural’ and ‘disaster’.

    2. In better responses, candidates correctly named a specific Australian disaster and explained how that disaster was caused by a combination of both natural and human activity. These candidates also linked both types of activity, showing cause and effect.

      Weaker responses stated a natural cause and a human cause without clearly relating the effects of both. Others simply stated a type of disaster, such as a bushfire.
  2. In better responses, candidates clearly described the necessary steps in locating the epicentre of an earthquake. They correctly explained the use of both graphs to determine the time difference between the P and S waves, and hence the distance from the epicentre. They stated the need for a radius to be drawn combining information from two other stations.

    Many responses made some reference to both graphs, but showed a poor understanding of the use of two graphs to locate the epicentre of an earthquake.

    1. In better responses, candidates gave two valid conclusions based on the table of results.

      In weaker responses, candidates gave only one correct conclusion.

    2. In better responses, candidates suggested three valid improvements to the experimental design. These included burning leaves at the same temperature, replication of the experiment, and controlling the leaf moisture content.

      In weaker responses, candidates proposed only one improvement to the experimental design. Many candidates suggested improvements that expanded the experiment rather than improved the investigation, such as the addition of more leaf types.
    1. In better responses, candidates described the weather changes that would occur at X as Y moves towards the west.

      In weaker responses, candidates described the weather conditions at X and at Y.

    2. In better responses, candidates clearly stated more than one named technology and provided reasons why each technology was an improvement in predicting weather changes.

      In weaker responses, candidates named more than one technology but did not include how each had improved weather predictions.
  5. In better responses, candidates provided a wide range of well-explained strategies that could be implemented before the fire season to minimise the effect of bushfires.

    In weaker responses, candidates provided a range of strategies with some explanation of how they work. Some candidates listed more than one strategy that could be used before the fire season.

Question 35 – Space Science

    1. In better responses, candidates identified two situations where a person would experience ‘weightlessness’ on Earth.

      Weaker responses identified only one situation. Others referred to ‘space’ situations.

    2. In better responses, candidates explained the circumstances that lead to weightlessness of an orbiting space station. This could include reference to the freefalling action around the Earth.

      Weaker responses referred to weightlessness as a result of a lack of gravity without relating it to the orbiting space station.
  2. In better responses, candidates stated the role of each component and justified the need for each.

    Weaker responses identified roles and/or reasons, but did not include information on all three components.

    1. In better responses, candidates made two relevant conclusions from the described experiment.

      Weaker responses made only one correct conclusion. Others only described the results.

    2. In better responses, candidates suggested three appropriate improvements to the experiment, which generally were linked to managing controlled variables.

      Weaker responses may have had one or two correct improvements. Some described improvements to reliability instead of validity.
  4. In better responses, candidates correctly described two pieces of new information about the universe collected by the Voyager 1 and 2 probes.

    In weaker responses, candidates gave one piece of new information discovered by the Voyager probes. Others described aspects of the universe not discovered by Voyager 1 or 2.

  5. In better responses, candidates described two improvements to a technology and related this to the quality of information produced about the universe.

    Weaker responses explained only one technology and the quality of its information. Others listed technologies or described or identified improved information collected.

  6. In better responses, candidates described problems that occur in space missions, their cause and their solution. They gave examples to explain aspects of each problem and used correct scientific terminology and logical sequencing.

    Weaker responses described one or a few problems in detail.
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